The overall goal of this proposal is to understand how cells are able to produce specific responses to changes in their microenvironment. Often, such responses involve G protein coupled receptors and thus are dependent on G protein signaling. G proteins transduce the extracellular signals received by receptors into cellular responses. Both the G? and the G[unreadable]? subunits of G proteins propagate signaling by activating/inhibiting various effector molecules which then cause changes in cell function. The first effectors discovered to be mediated by G[unreadable]? were the G protein coupled inwardly rectifying K+(GIRK) channels. Previous studies have shown that G[unreadable]? can mediate several effects on currents conducted by GIRK channels. Mutation of specific residues on the channel or G[unreadable]? may inhibit some G[unreadable]? effects but leave others intact. Thus this pro G[unreadable]? proposal hypothesizes that distinct interactions of G[unreadable]? and GIRK channels contribute to distinct effects of G[unreadable]? on GIRK currents. Specifically, G[unreadable]? -mediated effects on GIRK currents examined in this proposal are the stimulation of basal/agonist-induced currents and potentiation of Na+-induced currents. Simulations done in silico are used to predict pairs of interacting surface residues between the GIRK channel and G[unreadable]?. Validation of these predicted interaction sites and quantification of their relative contribution to various G[unreadable]? mediated effects on channel activity are accomplished through site directed mutagenesis and electrophysiological recordings. Findings will lead to a greater understanding of G protein signaling and the structural mechanism by which G[unreadable]? is able to independently control various activities of the same effector. G protein signaling is found ubiquitously throughout the body and controls various physiological phenomena. Most drugs sold today directly or indirectly modulate G protein signaling. Thus enhanced knowledge of the structural mechanisms underlying this signaling may reveal further targets for manipulation by therapy.